This section provides background information related to the present disclosure which is not necessarily prior art.
A sleeping bag typically includes first and second opposed halves defining a sleeping compartment therebetween and which are connected in such a way to define an entrance aperture at an entrance side or end of the sleeping bag. Each half of the sleeping bag includes an outer shell and an inner shell with an insulating material disposed and retained between these two layers. Insulation thickness depends on the minimum ambient air temperatures that are expected to be encountered by the user. Colder temperatures require a greater thickness of insulation to keep heat loss from the user sufficiently low enough that the user does not become uncomfortable. Sleeping bags come in several different physical configurations including, but not limited to, rectangular, semi-rectangular and mummy. In addition, many sleeping bags incorporate an integral hood. Typically, sleeping bags have one or more closure devices, such as zippers, of a selected length to provide access to the entrance aperture and which can be located on the sides, ends or top to permit use of the sleeping bag.
Cold weather sleeping bags normally incorporate integral hoods to minimize drafts and provide more insulation than is normally afforded using commonly available head covers. Often these cold weather bags also incorporate internal collars with draw cords that allow the collars to be snugged around the user's neck to further reduce drafts while also dividing the sleeping compartment into two distinct volumes, one for the body and one for the head. Since the hood is integral, the face opening is designed to be in a predetermined or “set” position relative to the user's face and mouth which is typically defined when the user is lying on his/her back. If the user wishes to sleep on their side or stomach they must turn the bag to retain the hood face opening in the proper position relative to the face. Thus, it is difficult to change positions while retaining the face opening in the set position relative user's face since the whole sleeping bag must be rotated. This is especially difficult in the confines of a small tent, as would normally be used in conjunction with such cold weather sleeping bags in mountaineering or backpacking applications. On the other hand, if the user rotates in the bag, which is a much simpler and easier proposition than rotating the whole bag, they will then be breathing into the interior of the bag with the face opening of the bag now at the side or back of their head. Breathing inside the bag is an unacceptable condition since it introduces significant amounts of moisture into the inside of the bag which, as it passes through the insulation, driven by the thermal gradient and air motion, condenses in the insulation, thus reducing the effectiveness of the insulation.